codegen/golang: emit any instead of interface{}

[kyleconroy]

Fixes #4470

Generated Go code now uses the predeclared any alias everywhere the generator previously wrote interface{}, so go fix has nothing left to change in sqlc's output.

Generator changes

• All four Go type mappers (postgresql_type.go, mysql_type.go, sqlite_type.go, go_type.go) return "any" for unknown/fallback types, and the stdlib/pgx templates (DBTX interfaces, exec/query/queryRow helpers, queryParams, batch/copyfrom value slices, enum Scan methods) spell the type any.
• The unknown-type backfill in result.go matches the new "any" spelling.
• any is added to the reserved identifier list, and query constant names are now escaped. This fixes a bug the switch would otherwise introduce: a query named Any generated const any = ..., which shadows the predeclared any type package-wide and no longer compiles once the surrounding code uses any. It now generates const any_ (the same _-suffix treatment other reserved identifiers get, which also covers previously-broken constants like const select).

Regenerated output

• All affected internal/endtoend/testdata golden directories (889 cases), with managed-db-only cases regenerated against a live PostgreSQL through the same config mutation TestReplay applies.
• All examples/.
• The six fixture files generation never overwrites (diff_output, diff_no_output, and expected-failure cases), plus the generated-code samples in docs/howto/.

Verification

• go fix itself skips files with a // Code generated ... DO NOT EDIT. header, so as proof both trees were copied with the markers stripped and run through go fix -diff on Go 1.26: zero diagnostics across all of internal/endtoend/testdata and examples, for every registered fixer (not just the any modernizer).
• Every golden-file change was verified to be purely the interface{} → any rewrite (no unrelated churn); the any case's const any_ rename is the one intentional exception.
• cd internal/endtoend/testdata && go build ./... passes, and the full suite go test --tags=examples -timeout 20m ./... passes against live PostgreSQL and MySQL, including TestReplay in both the base and managed-db contexts.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Pq9Cgx285AU4NZpCYgtkYS

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